The present invention relates to a method of dividing and exposing patterns. More particularly, the present invention relates to a method of dividing and exposing circuit patterns forming a liquid crystal display (LCD) with a plurality of divided patterns.
In recent years, liquid crystal displays have been used as display elements for personal computers, TV receivers, etc. in large quantities. Conventionally, the liquid crystal displays have been manufactured using glass substrates with photolithographically transferred circuit patterns.
A projection exposure apparatus is commonly used in an exposure process in which the images of circuit patterns are photolithographically transferred onto glass substrates. The exposure apparatus emits light from a light source for photolithographic transfer of the image through a reticle having liquid crystal display circuit patterns. Then it superimposingly projects the images of the circuit patterns by means of light going through the reticle onto a glass substrate via a projector lens system.
In this case, as illustrated in FIG. 12, a circuit pattern 1 of a liquid crystal display is formed in a rectangular shape consisting of a display section 2 and a peripheral portion 3 surrounding the display section 2. The display section 2 is a pattern in which a plurality of electrodes corresponding to a plurality of pixels of red, green, and blue are arranged regularly. The peripheral portion 3 comprises a plurality of, for example, trapezoidal interconnecting portions 4 (hereafter referred to as the "lead group") for connecting each of the electrode patterns with a plurality of drive circuits, not illustrated.
Recently, larger size liquid crystal displays have been in greater demand. The demand is met with the following step-and-repeat technique. When the size of a circuit pattern 1 of a liquid crystal display is larger than that of the effective diameter of the projection lens of the aforementioned exposure apparatus and larger than the area on which a reticle circuit pattern is formed (hereafter these sizes are referred to as "effective fields"), the circuit pattern 1 is divided into a plurality of types of patterns corresponding to the effective fields. In this case, a plurality of circuit patterns are formed by dividing a pattern (hereafter referred to as the "divided patterns") on a plurality of reticles. The images of the patterns of the reticles are then superimposingly photoprinted onto predetermined positions on each of the glass substrates in the exposure apparatus to transfer the circuit pattern 1 from the reticle onto the aforementioned glass substrate.
Now, as illustrated in FIGS. 13(A) and 13(B), when a liquid crystal display circuit pattern 1 is almost as large as the effective field, the aforementioned circuit pattern 1 is not divided FIG. 13(A)!, and the circuit pattern 1 is formed on a reticle 5 FIG. 13(B)!. The resist film on a glass substrate is superimposingly photoprinted relative to the circuit pattern 1 through the reticle 5 by "one exposure" processing in the exposure apparatus.
As illustrated in FIGS. 14(A) and 14(B), when the size of the circuit pattern 1 of the liquid crystal display is larger than the aforementioned effective field and up to about twice as large as the effective field, the aforementioned circuit pattern 1 is divided into divided patterns B and C Figure 14(A)! corresponding to the effective field to be transferred onto reticles 6A and 6B FIG. 14(B)!.
In this case, the exposure apparatus, for example, first photoprints the image of the left-half B of the divided circuit pattern 1 onto the resist film on the glass substrate through the reticle 6A; then, photoprints the image of the remaining right-half C of the divided circuit pattern 1 onto the resist film on the glass substrate through the reticle 6B. As such, in an exposure apparatus, the circuit pattern 1 is photolithographically transferred onto a resist film on a glass substrate using reticles 6A and 6B and two exposures.
As illustrated in FIGS. 15(A) and 15(B), when the circuit pattern 1 of a liquid crystal display is larger than the effective field by twice or more and less than about four times, the aforementioned circuit 1 is divided into four divided patterns D, E, F, and G Figure 15(A)! corresponding to the effective field. These divided patterns D through G are printed on reticles 7A, 7B, 7C, and 7D, respectively Figure 15(B)!.
The exposure apparatus first superimposingly photoprints the image of the upper left divided pattern D of the circuit pattern 1 onto a resist film on a glass substrate through a reticle 7A. Then the image of the upper right divided pattern E of the circuit pattern 1 is transferred onto the resist film on a glass substrate through a reticle 7B. After that it photoprints the image of the lower left divided pattern F of the circuit pattern 1 onto the resist film on the glass substrate through a reticle 7C. Finally, it photoprints the image of the lower right divided pattern G of a circuit pattern 1 onto a resist film on the glass substrate through a reticle 7D. As such, the exposure apparatus photolithographically transfers the circuit pattern 1 onto the resist film on the glass substrate using the reticles 7A, 7B, 7C, and 7D and four exposures.
Examples of this technique are described in U.S. Pat. Nos. 4,708,466 and 4,814,830.
Recently, however, a technique to increase manufacturing efficiency of a liquid crystal display has been introduced, namely the so-called "plural-area method." With this method, a plurality of liquid crystal display circuit patterns are photolithographically transferred onto an integral substrate to obtain a plurality of liquid crystal displays a so-called "plural-area production".
To apply the aforementioned step-and-repeat exposure in the plural-area production method, the lithographic pattern transfer can be performed by the number of exposures which is equal to the number of areas produced using each of the reticles having divided circuit patterns obtained by dividing a circuit pattern for the manufacture of a liquid crystal display.
When the size of such a liquid crystal display circuit pattern 1 is four times larger than that of the effective field, the aforementioned circuit pattern 1 is divided into a display section 2 and a periphery section 3 corresponding to the effective field, and the display section 2 and the periphery section 3 are divided further into smaller areas.
For example, as illustrated in FIG. 16(A), the display section 2 is divided into six even areas on the liquid crystal display circuit pattern 1.
In this case, because each of the electrode patterns in the display section 2 are relatively small and regularly arranged corresponding to each of the pixels, the display section 2 is divided into six almost identical divided patterns H.
Regarding the periphery section 3, each of the edges (hereafter referred to as "the first and the second edges") 3A and 3B arranged along the direction of the longer side of the circuit pattern 1 (hereafter simply referred to as "a longer side") are almost evenly divided into three sections. Also, each of the edges (hereafter referred to as "the third and the fourth edges") arranged in the direction perpendicular to the longer side are divided almost evenly into two sections.
In this case, in the periphery section 3, each of the lead patterns of the lead group 4 is relatively larger than each of the electrode patterns of the display section 2, and it is difficult to divide the periphery section 3 at the border of each of the adjacent lead groups 4, thus splitting the lead group 4 into two. Therefore, in the periphery section 3, the number of patterns increases because each of the divided patterns I, J, K, L, M, N, O, P, Q and R takes a different pattern.
For this reason, as illustrated in FIG. 16(B), when forming each of these divided patterns H through R onto a reticle 8, the conventional technique effectively uses the area of the surface on which divided circuit patterns H through R of the reticle 8 are formed. The divided pattern H is formed on a reticle 8A and each of the divided patterns, respectively, form a plurality of groups, I to K, L to N, and O to R to be, respectively, formed on each of the reticles 8B, 8C, and 8D. The technique decreases the number of reticles 8A through 8D required to accommodate the divided patterns H to R of a plurality of types.
Now, when superimposingly photoprinting using these reticles 8A, 8B, 8C, and 8D, the image of the display section 2 of the circuit pattern 1 is superimposingly photoprinted onto a glass substrate six times sequentially, first for example using the reticle 8A. Then using the reticles 8B, 8C, and 8D, the image of the periphery section 3 of the circuit pattern 1 is superimposingly photoprinted onto the glass substrate ten times sequentially while shutting off patterns other than the divided patterns required for exposure processing using a shutter plate.
Compared to a liquid crystal display having a circuit pattern size which is smaller than four times the size of the effective field, the liquid crystal display whose size of the circuit pattern 1 is larger by four times or more than the size of the effective field encounters a problem in that the number and the type of divided patterns I through R increase sharply. Also, the number and the types of exposure processing performed in an exposure apparatus increases sharply as well (sixteen times in the aforementioned case.) It also encounters a problem in that the throughput, the ability to process substrates per unit of time during exposure processing, decreases sharply.
Therefore, when a liquid crystal display circuit pattern 1 is four times or more larger than the effective field, the design of the reticle 8 has to take the number of divisions of the circuit into account, thus making difficult the designing of the aforementioned reticle 8.
In addition, the attempt to obtain plural divided areas of a liquid crystal display circuit pattern whose size is larger by four times or more than the effective fields of a projection lens system and reticles encounters problems of increasing the number of exposures and decreasing the throughput.
Plural divisions are produced basically to increase manufacturing efficiency of substrates. However, the attempt to print plural divided areas on an integrated substrate unfavorably increases the number of exposures, as mentioned, and decreases throughput. This is harmful in terms of efficiency.